It is known that restenosis can be defined as a recurrent reduction in the calibre of the coronary lumen at the site initially expanded with success during a coronary transluminal angioplasty.
This disorder remains the main current limitation on balloon coronary angioplasty since it leads to a new angioplasty in approximately 15 to 30% of cases within the 6 months following a successful angioplasty.
Various solutions have been envisaged to date for the prevention of restenosis, and these have led to more or less satisfactory results.
Thus, the use of so-called "ablative" angioplasty techniques such as, for example, laser angioplasty or atherectomy have not permitted a significant reduction in the incidence of restenosis.
In contrast, fitting a coronary endoprosthesis after angioplasty constitutes a relatively effective treatment in the prevention of restenosis, since it leads to a reduction by approximately 30% in the risk of restenosis.
However, the systematic fitting of endoprostheses cannot be envisaged, insofar as this could lead to operating unnecessarily on a large number of patients who would have suffered no restenosis without an endoprosthesis, and insofar as there would still be a relatively large number of patients suffering restenosis in spite of the fitting of an endoprosthesis.
Systemic administration of pharmacologically active substances such as antithrombins, converting enzyme inhibitors, some vasodilators or some hypolipidemic agents has to date not led to entirely satisfactory results.
This is why the use of devices intended for local delivery of therapeutically active substances constitutes a more promising prospect in the prevention of restenosis.
In fact, this method makes it possible to administer, at the dilated site, products which are specifically targeted against the mechanisms of restenosis, including products which are toxic for the rest of the body, in predetermined concentrations and over a variable period of time.
In order to be usable in the context of this method, the device must permit local delivery of the active substance without interruption to the flow of fluid in the bodily canal.
A catheter satisfying this requirement has been proposed in the document EP 0.526.102.
This catheter is generally composed of an elongate tubular element including an inflatable structure arranged at its distal part.
This inflatable structure consists of a set of identical toric balloons and a membrane fixed to these balloons, this structure being designed in such a way that, when it is inflated, it defines:
on the one hand, a central passage channel for the bodily fluid; and PA1 on the other hand, a substantially leaktight cavity or pouch, intended to contain said therapeutically active substance and defined by the balloons, by the outer surface of the membrane and by the inner surface of the bodily canal. PA1 a catheter body including an elongate tubular element having a proximal part and a distal part; PA1 an inflatable structure, arranged at the distal part of said catheter body and including: PA1 a membrane, fixed to said first and second inflatable elements and defining with them, when they are inflated;
The catheter body includes a first internal channel which communicates, on the one hand, with the balloons and, on the other hand, with a means making it possible to inflate and deflate these balloons; and a second internal channel which communicates, on the one hand, with the aforementioned cavity and, on the other hand, with a supply source of fluid containing a pharmacologically active substance.
As can be seen in the aforementioned document, in the diagrams illustrating the various embodiments of this catheter, the catheter body as well as the various intermediate balloons intended for holding the membrane in position are in direct contact with the bodily canal.
The result of this is that such a device does not make it possible to treat effectively, that is to say in a single operation, the entire surface of the bodily canal at the dilated site, since the active substance cannot reach the portion of the surface of the bodily canal which is in contact with the balloons and the catheter body, unless the inflatable structure is displaced, and this complicates the operation.